Heat-hardenable binder mixture

ABSTRACT

The heat-hardenable binder mixture based on organic resins comprises an organic resin having primary and/or secondary and, if appropriate, also additional tertiary amino groups and a cross-linking agent based on an organic compound containing at least 2 carbalkoxymethyl groups. The binder mixture can additionally contain pigments, fillers, cross-linking catalysts, corrosion inhibitors and further finish auxiliaries. The binder mixture is used in a process for preparing coatings by applying a coating agent in the form of a film to a substrate and subsequently hardening the film by baking.

BACKGROUND OF THE INVENTION

The invention relates to a heat-hardenable binder mixture based onorganic resins.

Many and varied chemical reactions have been proposed, and also used, toharden, by cross-linking, the binders in finish coatings. The chemicalbonds formed during the cross-linking reaction frequently do not satisfyall the requirements placed on the finish coatings. For instance, esterbonds are sensitive to hydrolysis, and amine groups form hydrophilicimperfections in the baked film.

In the two-component systems one of the reactive groups must frequentlybe blocked to prevent premature reaction.

In recent years, electrocoating has become widely established for thepriming of electrically conductive substrates. The emphasis has hithertobeen on anodic electropriming. The resin binders used for this purposebelong to the resins containing carboxyl groups, for example to themaleiate oils, maleiated epoxide resins, alkyd resins, acrylic resinsand, in particular, to the maleiated polybutadiens. These resins wererendered soluble in water by salt formation, chiefly with amines, anddeposited by the current at the anode in the electrocoating bath.However, the anodic electropriming process contains seriousdisadvantages. For instance, oxygen is evolved at the anode during theelectrical deposition and can modify the resins depositing at the anodein a serious, unfavourable manner. Furthermore, metal ions enter intosolution at the anode and are contained in the baked film asimperfections. The metal ions can lead to discoloration and spots. Theycause qualitative disadvantages in particular by salt formation andhence by reducing the resistance to water and the anti-corrosionprotection.

The cathodic electropriming process developed in recent years tocommercial maturity is increasingly displacing the anodic process, sincethe defects described above are largely avoided. For instance, hydrogen,which does not affect the resin binder, is formed during the depositionstep at the cathode, where the finish film is now deposited. Since thecathodic deposition can take place in the approximately neutral pHrange, there are hardly any metal ions going into solution. The binderssuitable for cathodic deposition contain predominantly amino groupswhich are neutralized with acids to obtain solubility in water.

However, a disadvantage is the fact that hydrophilic amino groups remainin the baked film and are responsible for a reduction of theanti-corrosion protection. Although the reaction of the amino groupswith blocked isocyanates in the cross-linking converted the amino groupsinto the less hydrophilic urethane group, blocking agents, such as, forexample, phenol or ketoximes, are liberated at the same time. Dependingon the type of structure of the amino group necessarily contained in theresin, these groups can also be thermally eliminated by β-elimination(German Offenlegungsschrift No. 2,363,074, and GermanOffenlegungsschrift No. 2,753,861). The resulting contamination of theoff-air by large amounts of eliminated protective groups of the blockedisocyanates and amines must also be considered a disadvantage of thisprocess.

SUMMARY OF THE INVENTION

The object of the invention is to avoid these disadvantages of the stateof the art and to provide a binder mixture for the preparation ofcoating agents which produce coatings having excellent technologicalproperties. The binder mixture according to the invention is intended toreduce environmental pollution when the corresponding coating agents areapplied.

This object is achieved according to the invention when a binder mixtureof the type mentioned at the outset comprises the components

(A) an organic resin having primary and/or secondary and, ifappropriate, also additional tertiary amino groups and

(B) a cross-linking agent based on an organic compound containing atleast two carboxymethyl ester groups.

The binder mixture, in addition to components A and B, advantageouslycontains, as component C, pigments, fillers, cross-linking catalysts,corrosion inhibitors and further finish auxiliaries.

Advantageously the content of component A is 50 to 95% by weight and ofcomponent B 5-50% by weight, the total amount of components A and Bbeing 100%.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

During the baking step, the carbalkoxymethyl ester groups of component Bnow react with the primary and/or secondary amino groups of component Ato form an amide bond. The basic nitrogen of the amino group of theresin of component A is thus converted in the baked film into apH-neutral amide nitrogen. The baked film thus contains fewer basicimperfections. The cross-linking mechanism is described in principle inthe following reaction scheme: ##STR1##

Virtually no amino groups are eliminated during baking, and off-airproblems are thus reduced. The hydroxyacetates eliminated advantageouslyhave a boiling point which is such that they can, with advantage, act asflow control agents during the baking step.

The amide bond formed during the baking has a very favourable effect onthe adhesion of the film, in particular to metal substrates. Theelasticity of the film is also increased by this fact. Thiscross-linking mechanism occasions high resistance of the finish film tosolvents, alkali and salt mist. Even on sheet iron not pretreated, thefilms form very resistant coatings even without corrosion inhibitors.

Component A of the binder mixture advantageously has a number averagemolecular weight of 500 to 20,000, preferably of 600 to 10,000. Theamine equivalent weight of component A of the binder mixture is 150 to7,500, preferably 200 to 5,000.

Component A is an organic resin having primary and/or secondary aminogroups. Tertiary amino groups can also be present in addition, ifappropriate.

The primary and/or secondary amino groups are preferably introduced intothe organic resin to prepare component A by reacting a polyamine and/oran amino- and/or hydroxyl-containing ketimene with resins containing atleast 1, preferably at least 2, epoxide groups or isocyanate groups permolecule.

Component A can, however, also be obtained by other addition reactions,for example by esterifying or amidating compounds carrying primaryand/or secondary amino goups with resins containing groups suitable forthis purpose.

Epoxide-containing resins having, preferably, terminal epoxide groupsfrom the group consisting of the polyglycidyl ethers, polyglycidylesters and polyglycidylamines are found to be particularly suitable forpreparing component A.

Other advantageously suitable epoxide-containing resins are copolymersof glycidyl acrylate and/or methacrylate or of another olefinicallyunsaturated, polymerizable compound carrying a glycidyl group with alkyland/or hydroxyalkyl acrylates and/or methacrylates, and/or vinylcompounds such as styrene, vinyltoluene or vinylcarbazole.

A further particularly suitable group of resins is partially epoxidizedpolybutadiene oils.

Polyglycidal ethers within the scope of this invention are understood asbeing preferably those polyglycidal ethers which have the generalformula ##STR2## with

R= ##STR3##

R¹ =H or C_(n) H₂ n+1

R² =(CR₂ ¹)n

R³ =R¹, halogen or, preferably H, and

n=0 to 5

Polyglycidyl ethers of the general formula shown have a number averagemolecule weight of about 340 to 5,000 and, accordingly, an epoxideequivalent weight of 170 to 2,500. The epoxide resins can also be usedin hydrogenated or partially hydrogenated form. To control filmproperties, some of the reactive groups of the epoxide resin can bereacted with other compounds. Suitable for this purpose are:

(a) carboxyl-containing compounds, such as saturated or unsaturatedmonocarboxylic acids (for example benzoic acid, linseed oil fatty acid,2-ethylhexoic acid, Versatic acid, aliphatic, cycloaliphatic and/oraromatic dicarboxylic acids of various chain lengths (for example adipicacid, sebacic acid, isophthalic acid or dimeric fatty acids),hydroxyalkylcarboxylic acids (for example lactic acid ordimethylolpropionic acid) and carboxyl-containing polyesters or

(b) amino-containing compounds such as diethylamine or ethylhexylamineor diamines having secondary amino groups, such as, for example,N,N'-dialkylenediamine, such as dimethylethylenediamine,N,N'-dialklpolyoxyalkyleneamine, such asN,N'-dimethylpolyoxypropylenediamine, cyano-alkylated alkylenediamines,such as bis-N,N'-cyanoethyl-ethyldiamine, cyanoalkylatedpolyoxyalkyleneamines, such asbis-N,N-cyanoethylpolyoxypropylenediamine, polyaminoamides such asVersamides or the reaction product of one mole of diaminohexane with twomoles of monoglycidylether or monoglycidyl ester, especially glycidylesters of α-branched fatty acids such as Versatic acid, or

(c) hydroxyl-containing compounds, such as neopentylglycol,bis-ethoxylated neopentyl glycol, neopentyl glycol hydroxypivalate,dimethylhydantoin-N,N'-diethanol, 1,6-hexanediol,2,5-hexanediol,but-2-ene-1,4-diol, but-2-yne-1,4-diol, hex-3-yne-2,5-diol or otheralkynediols, 1,4-bis-(hydroxymethyl)-cyclohexane,1,1-isopropylidene-bis-(p-phenoxyl)-2-propanol, trimethylolpropane,pentaerythritol or amino-alcohols, such as triethanolamine,methyldiethanolamine or hydroxyl-containing alkylketimines, such asaminomethyl propane-1,3-diol-methyl isobutylketimine ortris-(hydroxymethyl)-aminomethane-cyclohexaneketimine, and alsopolyglycol ethers, polyesterpolyols, polyetherpolyols, orpolycaprolactonepolyols of various functionality and molecular weights.

Instead of using polyglycidyl ethers based on bisphenol A it is alsopossible to use polyglycidyl ethers based on other parent components,such as triglycidyl isocyanurate, heterocyclic diglycidyl compounds ofdiglycidyl hydantoins.

Suitable polyglycidyl esters are reaction products of, for example,bis-glycidyl terephthalate or bis-glycidyl isophthalate with, forexample bisphenol A. The epoxide equivalent weight of these products isbetween 200 and 2,500. To control film properties, some of theremaining, reactive glycidyl groups can be reacted with other compounds.The compounds mentioned above under a, b and c are suitable for thatpurpose.

Polyglycidylamines are understood as meaning those glycidyl-containingresins obtained by introducing glycidyl groups via, for example,epichlorohydrin into NH₂ -functional resins.

Copolymers of glycidyl acrylate and/or methacrylate or of anotherolefinically unsaturated, polymerizable compound carrying a glycidylgroup with esters of acrylic and/or methacrylic acid and polymerizablevinyl compounds having a number average molecular weight of 700 to10,000 and an epoxide equivalent weight of 600 to 3,000 are alsoparticularly suitable. Acrylates with C₂ -to C₈ -alcohols andmethacrylates with C₁ -to C₄ -alcohols are preferable. The copolymerscan contain further monomers, such as hydroxyalkyl(meth)acrylate or(meth)acrylamide. The copolymerization is effected in a well known wayby solution, suspension or emulsion polymerization with the addition offree-radical initiators, such as peroxides, hydroperoxides, peresters orthermolabile azo compounds, and, if appropriate, molecular weightregulators.

Partially epoxidized polybutadien oils are understood as meaningreaction products obtained by reacting commercially availablepolybutadieno oils with peracids or with organic acid/H₂ O₂ mixtures.The preparation method has been described, for example inChemiker-Zeitung 95, 857 et seq (1971).

The epoxide-containing resins are reacted with polyamines and/or anamino- and/or hydroxyl-containing ketimine. If the addition of compoundscarrying primary and secondary amino groups is carried out in the formof their ketimines, the reaction conditions are to be controlled in sucha way that no substances decomposing the ketimines remain in thereaction product. The preferable ketimines are reaction products ofketones and alkylamines or alkyldiamines containing hydroxyl orsecondary amino groups and having the general structure ofR--NH--R'--NH₂ or HO--R--NH₂ respectively. The ketimines have, forexample, the following structure: ##STR4## where

X=--(CR₂)_(n) --

R=--H, --R'

R'=--C_(m) H_(2m+1), --C₆ H₁₁

U=--R, --Y

Y= ##STR5##

Z=>CO, --X

n=1-6 and

m=1-12

The ketones used for the reaction with the primary amino groups aregenerally aliphatic ketones, such as methyl ethyl ketone, diethylketone, methyl isobutyl ketone or ethyl n-propyl ketone, andcycloaliphatic ketones, such as cyclopentanone and cyclohexanone. Thepreferable amino alkylamines and alkanolamines are chieflydiethylenetriamine, N-methylethylenediamine, N-methylpropylenediamine,N-aminoethylpiperazine, 2-aminoethanol, 1-aminopropan-2-ol,1-aminopropan-3-ol, 2-amino-2-methyl propan-1-ol, 3-amino-2,2dimethylpropan-1-ol, 1,5-diaminopentan-3-ol orN-(2-aminoethyl)-N-(2-hydroxyethyl)-ethylenediamine.

The exothermal addition of the amino ketimines described above to theepoxide groups of the base resin of binder component A is in generaleffected at room temperature. For complete conversion, the reaction isfrequently completed at temperatures between 50° and 125° C.

The addition of the hydroxyketimines to the epoxide groups of the baseresin of binder component A is as a rule carried out within the sametemperature range, but the use of a basic catalyst, such asN,N-dimethylbenzylamine or of a Friedel-Crafts catalyst such astin-II-chloride, is advisable.

It is also possible to use base resins having at least 2 isocyanategroups as the base resin of binder component A. Preferable resinscontaining isocyanate groups are higher-functional polycyanates preparedby trimerization or oligomerization from diisocyanates orpolyisocyanates and polyfunctional compounds containing OH or NH groups.Typical isocyanates are toluylene diisocyanates, hexamethylenediisocyanates, 4,4'-diphenylmethane diisocyanate,4,4'-dicyclohexylmethane diisocyanate,1,6-diisocyanato-2,2,4-trimethylhexane and1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane.Isocyanate-containing prepolymers based on polyglycol ethers,polyesteripolyols, polyetherpolyols, polycaprolactonepolyols orpolyaminoamides can also be used with advantage.

Binder component B, the cross-linking agent, is a compound whichcontains at least 2 carbalkoxymethyl ester groups. The cross-linkingagent can be a low molecular weight compound or a correspondinglysubstituted resin. If an alcohol without a carbalkoxy group, such asmono-alcohols such as methyl, ethyl or butyl alcohol, is used for theesterification, the amidation reaction proceeds too slowly.

The cross-linking rate in this case is too low, and the baked film isnot sufficiently resistant to solvents. These disadvantages arecircumvented, when, in accordance with the invention, carbalkoxymethylesters are used for the amidation reaction. The compounds which form thecross-linking agent are preferably polyester resins, but it is alsopossible to use other compounds containing free carboxyl groups to whichthe carbalkoxymethyl groups can become attached. These compounds canalso contain primary, secondary or tertiary nitrogen atoms to beprotonated with acid. In order for the resins to become soluble inwater, they can also be modified with ammonium groups or by sulfide/acidor phosphine/acid mixtures.

The amidation components preferably used arepoly(carbalkoxymethyl)esters of polycarboxylic acids. These include,inter alia,

bis-(carbalkoxymethyl) azelate

bis-(carbalkoxymethyl) sebacate

bis-(carbalkoxymethyl) adipate

bis-(carbalkoxymethyl) decanate, and

bis-(carbalkoxymethyl) terephthalate

Polyfunctional cross-linking agents can also be advantageously preparedin the following way. First, equivalent amounts of a dicarboxylicanhydride (phthalic anhydride, hexahydrophthalic anhydride, trimelliticanhydride, or succinic anhydride) are reacted with a polyol (glycerol,trimethylolpropane, pentaerythritol or dipentaerythritol) attemperatures below 145° C. The acidic intermediate product formed isthen reacted by generally known methods, to which this invention doesnot relate, to give carbalkoxymethyl esters.

Component B is advantageously a polyacrylate resin of the followingmonomers:

(a) 10-50% by weight of alkyl acrylate having 1 to 18 carbon atoms inthe alkyl radical and/or alkyl methacrylate having 2-18 carbon atoms inthe alkyl radical,

(b) 0-60% by weight of methyl methacrylate,

(c) 0-35% by weight of styrene, α-methylstyrene, o- and/orp-chlorostyrene, p-tert.-butylstyrene, vinyltoluene and/orvinylcarbazole and

(d) 2-65% by weight of carbalkoxymethyl methacrylate and/orcarbalkoxymethyl acrylate or of another olefinic, unsaturatedpolymerizable compound containing carbalkoxymethyl ester groups, thetotal amount of constituents a, b, c and d being 100%.

The binder mixture according to the invention can be present in finelydivided, solid form or dissolved in an organic solvent.

For electrocoating, it is necessary that the binder mixture, afterprotonation with acid, is present in the form of an aqueous solution ordispersion. The solubility in water of the binder component and/or ofthe cross-linking component is effected by neutralizing with acids theprimary, secondary and/or tertiary amino groups contained therein.Suitable acids are in particular organic acids, but it is also possibleto use, for example, hydrochloric acid or phosphoric acid. The aminogroups are preferably neutralized with formic acid, acetic acid, malonicacid, lactic acid or citric acid.

The acids mentioned can also be used when the solubilizing groups forthe binder component and/or the cross-linking component are introducedby adding an ammonium group or the salt of a sulfide/acid orphosphine/acid mixture to the binder or the cross-linking agent.

The degree of neutralization of the solubilizing groups is, relative tothese groups, between 0.2 and 1.0 equivalent, preferably between 0.25and 0.6 equivalent, of acid.

The neutralization can also be carried out as follows. The acid isinitially introduced in water, if appropriate together with dispersingauxiliaries, and the resin solution is stirred into the water at roomtemperature or, if appropriate, at elevated temperatures. However, theacid can also be added directly to the resin solution. The neutralizedresin solution can then be stirred into the water, but, if appropriate,the water can also be slowly incorporated in the resin solution.

The dispersion, to control its viscosity, the deposition voltage andflow, can contain up to 20% of organic solvents. If the batch containstoo much solvent, due to the preparation method chosen, or even solventharmful to the properties, these solvents can be distilled from theresin solution before the dispersing or they are distilled from theaqueous dispersion. A proportion of organic solvents which is as low aspossible is advantageous for the sum of all properties.

The solids content of a deposition bath made up with the dispersionaccording to the invention, is 7-35 parts by weight, but preferably12-25 parts by weight. The pH value of the deposition bath is between 4and 8, but preferably between 5 and 7.5. Non-corroding steel anodes orgraphite anodes are used as the anodes of the deposition bath. Thetemperature of the made-up bath should be between 15° and 35° C.,preferably between 20° and 30° C. The deposition time and voltage are sochosen that the layer of thickness desired is obtained.

After the deposition, the coated article is rinsed off and is ready forbaking.

Regardless of the application method of the coating agent prepared onthe basis of the binder mixture according to the invention, the finishfilm is cross-linked during baking at temperatures of 130° to 200° C.for a period of 10-60 minutes, preferably at 150° to 180° C. for 15-30minutes.

The amidation reaction can be further accelerated by suitable catalysts.Catalysts suitable for this purpose are in particular ammonium compoundssuch as benzyltrimethylammonium hydroxide, benzyltrimethylammoniumchloride, trimethylcetylammonium bromide or tetraammonium iodide andorganic tin compounds, such as dibutyltin dilaurate, and iron(III)acetylacetonate, zinc acetate, zinc 2-ethylhexoate, cobalt naphthenate,lead acetate or butyl titanate.

Pigmentation is effected in a well-known way. In this step, the pigmentsas well as customary additives, such as fillers, corrosion inhibitorsand anti-foam agents, are incipiently milled in one of the two bindercomponents. Possible milling units are, for example, sand mills, ballmills or three-roll mills. The finish can be completed in a generallyknown manner.

Individual components A and B and, if appropriate, component C can bemixed in the form of their concentrated solutions and conjointlydispersed. However, it is also possible to disperse components A and Bindividually, in which case the pigments have been incipiently ground inA or B, and to mix the dispersion of the individual components in theratio necessary.

The invention also relates to a process for preparing coatings bybaking, by applying a coating agent in the form of a film to asubstrate, where the coating agent contains a binder mixture comprisingthe mixture of two components

(A) an organic resin having primary and/or secondary and, ifappropriate, also additional tertiary amino groups and

(B) a cross-linking agent based on an organic compound containing atleast two carbalkoxymethyl ester groups.

Advantageous embodiments of the process according to the invention areas follows:

(1) the mixture, in addition to components A and B, contains, ascomponent C, pigments, fillers, cross-linking catalysts, corrosioninhibitors and further finish auxiliaries;

(2) the content of component A is 50-95% by weight and of component B5-50% by weight, the total amount of components A and B being 100%;

(3) component A has a number average molecular weight of 500 to 20,000;

(4) component B has a number average molecular weight of 200 to 10,000;

(5) component B is a polyacrylate resin of the following monomers:

(a) 10-50% by weight of alkyl acrylate having 1 to 18 carbon atoms inthe alkyl radical and/or alkyl methacrylate having 2-18 carbon atoms inthe alkyl radical;

(b) 0-60% by weight of methyl methacrylate;

(c) 0-35% by weight of styrene, α-methylstyrene, o- and/orp-chlorostyrene, p-tert.-butylstyrene, vinyltoluene and/orvinylcarbazole; and

(d) 2-65% by weight of carbalkoxymethyl methacrylate and/orcarbalkoxymethyl acrylate or of another olefinic, unsaturatedpolymerizable compound containing carbalkoxymethyl ester groups, thetotal amount of constituents (a),

(b), (c) and (d) being 100%;

(6) the coating agent is present in finely divided, solid form;

(7) the coating agent is applied by an electrostatic powder spraydevice;

(8) the binder mixture is present dissolved in an organic solvent;

(9) the coating agent is applied by spraying, dip-coating, flow-coating,roll-coating, knife-coating, or the like; and

(10) an electrically conductive substrate is immersed in an aqueous bathwhich contains a coating agent which is at least partially neutralizedby acid and which, if appropriate, additionally contains organicsolvents, and is connected as the cathode, the film is deposited on thesubstrate by means of direct current, the substrate is removed from thebath, and the film is hardened by baking.

The invention also relates to the use of a binder mixture for preparingcoatings, which comprises the mixture of components

(A) an organic resin having primary and/or secondary and, ifappropriate, also additional tertiary amino groups and

(B) a cross-linking agent based on an organic compound containing atleast two carbalkoxymethyl ester groups.

Advantageous embodiments of their use according to the invention are asfollows:

(1) the mixture, in addition to components A and B contains, ascomponent C, pigments, fillers, cross-linking catalysts, corrosioninhibitors and further finish auxiliaries;

(2) the content of component A is 50-95% by weight and of component B5-50% by weight, the total amount of components A and B being 100%;

(3) component A has a number average molecular weight of 500 to 20,000;

(4) component B has a number average molecular weight of 200 to 10,000;

(5) component B is a polyacrylate resin of the following monomers:

(a) 10-50% by weight of alkyl acrylate having 1 to 18 carbon atoms inthe alkyl radical and/or alkyl methacrylate having 2-18 carbon atoms inthe alkyl radical,

(b) 0-60% by weight of methyl methacrylate

(c) 0-35% by weight of styrene, α-methylstyrene, o- and/orp-chlorostyrene, p-tert.-butylstyrene, vinyltoluene and/orvinylcarbazole, and

(d) 2-65% by weight of carbalkoxymethyl methacrylate and/orcarbalkoxymethyl acrylate or of another olefinic, unsaturatedpolymerizable compound containing carbalkoxymethyl ester groups, thetotal amount of constituents (a), (b), (c) and (d) being 100%;

(6) the binder mixture is present in finely divided, solid form and isused for powder finishes;

(7) the binder mixture is present dissolved in an organic solvent and isused for baking finishes;

(8) the binder mixture, after protonation with acid, is present in theform of an aqueous solution or dispersion and is used for cathodicelectrocoating; and

(9) the finely divided, solid form is used for aqueous powder slurries.

Below, the invention is illustrated in more detail by means ofillustrative embodiments.

EXAMPLE 1 Preparation of a tetrafunctional cross-linking agent

109 g of pentaerythritol are mixed with 474 g of phthalic anhydride in a4-necked flask equipped with a reflux condenser, stirrer, internalthermometer and gas inlet tube, and the mixture is heated under nitrogento 140° C. The reaction then proceeds exothermally and is maintained at160° C. by cooling. The batch is cooled down to room temperature at anacid number of 305, and 300 g of acetone are added. 81 g oftriethylamine are then added, and 98 g of ethyl chloroacetate are addeddropwise. The mixture is then heated to reflux temperature. Thetemperature is maintained for 4 hours, and the batch is then allowed tocool down. The triethylammonium chloride formed is filtered off after 12hours. The acetone is removed from the filtrate in a rotary evaporator.

EXAMPLE 2 Preparation of a polyfunctional cross-linking agent

142 g of trimethylolpropane, 723 g of caprolactone and 600 g ofmethylisobutyl ketone are initially introduced into a reaction vesseland heated to reflux temperature. 609 g of trimellitic anhydride areadded after 6 hours. When the acid number of 228 has been reached, thebatch is cooled down to 50° C., a further 600 g of methyl isobutylketone are added, and 641 g of triethylamine are slowly added dropwise.The temperature is maintained at 60° C. by cooling. 685 g of methylchloroacetate are then added. The reaction is carried out for 4 hours at60° C. The batch is then cooled down to room temperature and the saltformed is filtered off. The solids content of the cross-linking resin is70%.

EXAMPLE 3 Preparation of a polyfunctional cross-linking agent based on apolyacrylate resin

560 g of xylene are initially introduced under nitrogen into a 5 lreactor and heated to reflux temperature. A monomer mixture of 1,400 gof methyl methacrylate, 560 g of carbethoxymethyl methacrylate, 840 g ofethylene hexyl methacrylate and 14 g of dodecylmercaptan are addeddropwise in the course of 4.5 hours. 140 g of tert.-butyl peroctoate and200 g of xylene are metered in at the same time. The batch is thenpolymerized until a constant viscosity of 4.0 dPa.s, 50% strength inxylene, has been reached. The solids content is then adjusted withxylene to 70%.

The number average molecular weight, measured by gel permeationchromatography against a polystyrene standard, is 2,100.

EXAMPLE 4 Preparation of a dispersion of component A

1,188 parts by weight of bis-(4-hydroxycyclohexyl)-2,2-propanebisglycidyl ether, 308 parts by weight of bisphenol A, 675parts by weight of polytetrahydrofuran (molecular weight 1,000) and 189parts by weight of xylene are initially introduced into a 4 l reactor. 5parts by weight of dimethylbenzylamine are added as a catalyst. Themixture is heated to 170° C. and maintained at this temperature for halfan hour. The mixture is then cooled down to 136° C., and a further 10parts by weight of dimethylbenzylamine are added. The temperature ismaintained until an epoxy equivalent weight of 1,500 is reached. Thebatch is then cooled down to 85° C., and 725 parts by weight of the 70%strength cross-linking solution (Example 2) are added. The temperatureis allowed to increase again to 85° C., and 515 parts by weight of a 70°strength solution of 1 mole of diethylene triamine and 2 moles of methylisobutyl ketone are added. The batch warms up during this addition. Thetemperature is maintained between 95° and 100° C. for 60 minutes byexternal cooling.

In the meantime a mixture of 4,070 parts by weight of deionized water,81 parts by weight of acetic acid and 21 parts by weight of acommercially available defoamer has been prepared. The resin describedabove is then dispersed in this mixture. The dispersion has a solidscontent of 40% and a degree of neutralization of the amine groups of33%. A further 970 parts by weight of water are added after an hour toestablish a solids content of 35%.

EXAMPLE 5 Preparation of a pigment paste containing component A, for anelectrocoating bath

The batch described in Example 4, to prepare an organic resin, isrepeated, but discontinued before the dispersing step and worked up asfollows. For this purpose, a water/acetic acid mixture (162 g of aceticacid plus 64 g of water) is added to the batch to effect 100%neutralization of the amine groups. A solids content of 50% is thenestablished with deionized water.

The pigment paste is prepared from the following components:

2,380 g of 50% strength resin solution

1,600 g of charcoal dust

200 g of lead silicate

1,200 g of deionized water

The starting materials are comminuted in a grinding unit to a Hegmanfineness of 6 to 7. A further amount of deionized water is then added toobtain the consistency desired. The pigment paste has a solids contentof 56.1%, a resin content of 21.8% and a pigment solids content of34.3%. The paste has excellent thermal stability on storage.

EXAMPLE 6 Preparation of an electrocoating bath

2,434.5 g of deionized water are added to 287.5 g of the binderdescribed in Example 4 and 178 g of the pigment paste described inExample 5. The solids content of the deposition bath resulting from themixture is 16%. The pH value is 7.5%. The breakthrough voltage of thebath is 370 to 380 v. Steel sheets treated with zinc phosphate arecoated for 120 seconds at a bath temperature of 25° C. and at a voltageof 300 volts. This produces continuous films which, after 20 minutesbaking at 160° C., afford a smooth, firmly adhering layer of 30 μm.

EXAMPLE 7 Preparation of a dispersion of component A

In a 6 l reactor, 1,453 g of a 90% strength solution of the ketimine ofmonoisopropanolamine and methyl ethyl ketone, in methyl ethyl ketone,are added to 3,380 g of partially epoxidized polybutadien (molecularweight 2,600, 4.8% weight of epoxide oxygen), and 32.5 g of phenol areadded as catalyst. The mixture is heated to 160° C. and maintained atthis temperature until epoxide oxygen is no longer detectable. The batchis then cooled down to 90° C., and a solution, adjusted to a solidscontent of 70%, of the cross-linking agent of Example 3 is added. Thecrosslinking agent solution is mixed in for 15 minutes. The batch isthen dispersed in a mixture of 6,210 g of deionized water, 281 g oflactic acid and 55 g of a commercially available defoamer. Thedispersion has a solids content of 40% and a degree of neutralization ofthe amine groups of 40%.

EXAMPLE 8 Preparation of a pigment paste

146 g of a reaction product of an epoxide resin having an epoxideequivalent weight of 890 and diethanolamine/lactic acid salt areinitially introduced together with 199 g of deionized water. 200 g ofTiO₂, 48 g of extender based on aluminum silicate, 11 g of lead silicateand 3 g of carbon black are added. The starting components arecomminuted in a grinding unit to a Hegman fineness of 5-7. A further 102g of deionized water are then added to obtain the paste consistencydesired. The grey pigment paste has a very long shelf life.

EXAMPLE 9 Preparation of an electrocoating bath

500 parts by weight of the binder dispersion described in Example 7 and196 parts by weight of the pigment paste described in Example 8 aremixed with 804 parts by weight of deionized water. The content ofnon-volatile fractions in the made-up bath is 20%. This deposition bathhas a pH value of 6.2. Films deposited on zinc-phosphatized metal sheetsfor 2 minutes at 300 volts and baked for 30 minutes at 170° C. have asmooth, hard non-yellowed surface. The film thickness is 25 μm. Theadhesion to the metal sheets is excellent.

I claim:
 1. A process for preparing coatings by applying a coatingcomposition to a substrate and subsequently hardening the resulting filmby baking at temperatures of 130° to 200° C. for a period of 10 to 60minutes to cross-link the film, wherein the coating composition containsa binder mixture of components comprising:(A) 50 to 75% by weight of anorganic resin having primary and/or secondary amino groups, a numberaverage molecular weight of 500 to 20,000 and an amine equivalent weightof 150 to 7,500; and (B) 5 to 50% by weight of a cross-linking agentbased on an organic compound containing at least two carbalkoxymethylester groups, said organic compound selected from the group consistingof polyester resins and compounds containing free carboxyl groups towhich said carbalkoxymethyl can be attached, the total amount ofcomponents A and B being 100%.
 2. A coated substrate from a coatingcomposition containing a binder mixture of components, comprising:(A) 50to b 95% by weight of an organic resin having primary and/or secondaryamino groups, a number average molecular weight of 500 to 20,000 and anamine equivalent weight of 150 to 7,500; and (B) 5 to 50% by weight of across-linking agent based on an organic compound containing at least twocarbalkoxymethyl ester groups, said organic compound selected from thegroup consisting of polyester resins and compounds containing freecarboxyl groups to which said carbalkoxymethyl can be attached, thetotal amount of components A and B being 100%, said composition hardenedto a resulting film by baking at temperatures of 130° to 200° C. for aperiod of 10 to 60 minutes to cross-link the film.
 3. The process ofclaim 1, wherein said resulting film is baked at a temperature of 150°to 180° C. for 15 to 30 minutes and component A has a number averagemolecular weight of 600 to 10,000 and an amine equivalent weight of 200to 5,000 .
 4. The coated article of claim 2, wherein said resulting filmis baked at a temperature of 150° to 180° C. for 15 to 30 minutes andcomponent A has a number average molecular weight of 600 to 10,000 andan amine equivalent weight of 200 to 5,000.
 5. The process of claim 1,wherein the mixture contains in addition to components A and B acomponent C comprising pigments, fillers, cross-linking catalysts,corrosion inhibitors and further finish auxiliaries.
 6. The process ofclaim 1, wherein component B has a number average molecular weight of200 to 10,000 .
 7. The process of claim 6, wherein component B is apolyacrylate resin of the following monomers:(a) 10-50% by weight ofalkyl acrylate having 1 to 18 carbon atoms in the alkyl radical, alkylmethacrylate having 2-18 carbon atoms in the alkyl radical and mixturesthereof; (b) 0-60% by weight of methyl methacrylate; (c) 0-35% by weightof styrene, α -methylstyrene, o-chlorostyrene, p-chlorostyrene,p-tert.-butylstyrene, vinyltoluene, vinylcarbazole and mixtures thereof;and (d) 2-65% by weight of carbalkoxymethyl methacrylate,carbalkoxymethyl acrylate, another olefinic, unsaturated polymerizablecompound containing carbalkoxymethyl ester groups and mixtures thereof,the total amount of constituents (a), (b), (c) and (d) being 100%. 8.The process of claim 6, wherein the coating agent is present in finelydivided, solid form.
 9. The process of claim 6, wherein the bindermixture is present dissolved in an organic solvent.
 10. The coatedarticle of claim 2, wherein the mixture contains in addition tocomponents A and B a component C comprising pigments, fillers,cross-linking catalysts, corrosion inhibitors, and further finishauxiliaries.
 11. The coated article of claim 2, wherein components B hasa number average molecular weight of 200 to 10,000.
 12. The coatedarticle of claim 11, wherein component B is a polyacrylate resin of thefollowing monomers:(a) 10-50% by weight of alkyl acrylate having 1 to 18carbon atoms in the alky radical, alkyl methacrylate having 2-18 carbonatoms in the alkyl radical, and mixtures thereof; (b) 0-60% by weight ofmethyl methacrylate; (c) 0-35% by weight of styrene, α-methylstyrene,o-chlorostyrene, p-chlorostyrene, p-tert.-butylstyrene, vinyltoluene,vinylcarbazole and mixtures thereof; and (d) 2-65% by weight ofcarbalkoxymethyl methacrylate, carbalkoxymethyl acrylate, anotherolefinic, unsaturated polymerizable compound containing carbalkoxymethylester groups and mixtures thereof, the total amount of consitituents(a), (b), (c) and (d) being 100%.
 13. The coated article of claim 11,wherein the binder mixture is present dissolved in an organic solvent.14. The coated article of claim 13, having baking finishes.